1. Field of the invention
The present invention relates to a connecting shaft mechanism of a caster assembly, more particularly one, which is easy to manufacture and assemble, and which is structured such that various parts thereof are securely connected together.
2. Brief Description of the Prior Art
Casters that are used on trolleys and hospital beds, such as is shown in FIG. 7, usually include a wheel, an immobilizing mechanism for the wheel, a connecting shaft mechanism, by means of which the wheel is held in position, and a control mechanism usable for activating the immobilizing mechanism; both the immobilizing mechanism and the control mechanism are connected with the connecting shaft mechanism.
Referring to FIG. 5, a conventional connecting shaft mechanism of a caster assembly includes a connecting shank member 82, and a sleeve, which consists of two sleeve half parts 81, 81. The supporting shank member 82 has an axial hole, annular recesses 821, annular protrusions 822 adjacent to the annular recesses 821, and a radial through hole 823. The sleeve half parts 81 have fitting posts 811 and fitting cavities 812 on upper portions of inward flat sides thereof, radial through holes 814, holding recesses 813 on upper portions, lengthwise extending recesses 816 under and communicating with the holding recesses 813, inward semicircular protrusions 817 and semicircular recesses 818 at lower portions, and stopping protrusions 815 adjacent to uppermost portions of the holding recesses.
The sleeve half parts 81, 81 are coupled to become the sleeve with the fitting posts 811 being respectively fitted in the fitting cavities 812, and the supporting shank member 82 is connected with the sleeve with the annular protrusions 822 thereof being fitted in the semicircular recesses 818 of the sleeve half parts 81, and the annular recesses 821 thereof being fitted over the semicircular protrusions 817 of the sleeve half parts. And, a metallic ring 83 is tightly fitted around upper extensions of the coupled sleeve half parts 81, 81 for holding the same together. Furthermore, the radial through holes 814, 823 of the sleeve half parts 81 and the shank member 82 are aligned with each other, and pins are inserted into the radio through holes 814 and 823; thus, the sleeve half parts 81, 81 are more firmly held together, and the supporting shank member 82 can't be separated from or angularly displaced relative to the sleeve.
The control mechanism is connected with the sleeve with a turning element 84 thereof being held in both of the holding recesses 813 of the sleeve half parts, the angular displacement of which turning element 84 is limited by means of the stopping protrusions 815 of the sleeve half parts.
The connecting shaft mechanism has advantages as followings:
1. The pins are used to prevent angular displacement of the shank member relative to the sleeve half parts, therefore in assembly, the assembler has to move the shank member carefully to such a position that the radial through holes are aligned with corresponding through holes of the sleeve half parts for allowing insertion of the pins into the through holes. Consequently, the connecting shaft mechanism takes much labor and time to assemble.
2. Because the sleeve half parts have to be formed with upper extensions for connection with the metallic ring, which is used to hold the sleeve half parts together besides the pins, the sleeve half parts have increased length, and more materials have to be used in manufacturing them. Consequently, the material cost increases. And, there will be an additional step in assembling the connecting shaft mechanism.
3. The pins and the metallic ring need to be manufactured with their respective processes therefore there are too many steps in manufacturing the caster assembly. Consequently, the manufacturing cost of the whole caster assembly will increase significantly.
4. Because of the stopping protrusions of the sleeve half parts, which are used to limit the angular displacement of the turning element in the holding recesses, the sleeve half parts will be more difficult to manufacture.
Referring to FIG. 6, another conventional connecting shaft mechanism of a caster assembly includes upper and lower hollow supporting shanks 91 and 92, and a sleeve, which consists of two sleeve half parts 93, 93. The upper supporting shank 91 is held in an upper end of the lower supporting shank 92 at a lower end thereof, and has a holding room in an upper portion thereof, and two radial through holes, which oppose each other, on two sides of the holding room. The sleeve half parts 93 have holding recesses 931 on inward sides thereof, stopping protrusions 932 adjacent to uppermost portions of the holding recesses 931, and through holes communicating with the holding recesses, and they are coupled with the holding recesses 931 facing each other. A turning element 94 of a control mechanism is held in the holding recesses 931, and the sleeve is closely fitted in the holding room of the upper supporting shank 91, and a lever (not shown) of the control mechanism is connected with the turning element 94 after having been passed through the through holes of the sleeve half parts 93 and the upper supporting shank 91. Furthermore, an adjusting element of an immobilizing mechanism (not shown) is passed into both the lower and the upper supporting shanks 91 and 92 to be right under the turning element 94 of the control mechanism. And, the upper end of the upper supporting shank 91 is folded inwards by means of pressing rollers such that it is pressed against the sleeve half parts 93, 93. Consequently, the sleeve half parts 93 are firmly held in the holding room of the upper supporting shank 91.
The second connecting shaft mechanism has advantages as followings:
1. The upper supporting sank has be formed with the radial through holes for allowing the lever to be connected with the turning element held in the sleeve, and in assembly, the assembler has to position the sleeve carefully such that the through holes of the sleeve half parts are aligned with the radial through holes of the. Therefore, the connecting shaft mechanism takes more labor and time to assemble.
2. The upper supporting shank will be reduced in the length after the upper end thereof is inwards folded onto the top of the sleeve by means of pressing rollers. Therefore, the pressing process has to be carefully performed otherwise the upper supporting shank can't be formed with proper length. Furthermore, owing to the pressing process with rollers, the connecting shaft mechanism will be more difficult to manufacture no matter which one of both the sleeve and the immobilizing mechanism is connected with the upper supporting shank first.
3. The pressing process with rollers isn't relatively easy, and in turns, it will cause increase to the cost and time needed to manufacture the caster assembly.
4. The sleeve half parts also have to be formed with the stopping protrusions, which are used to limit the angular displacement of the turning element held in the holding recesses. Therefore, the sleeve half parts are as difficult to manufacture as those of the first conventional shaft mechanism.